1. Field
This invention relates to use of stimuli-responsive highly superabsorbent polymers for harvesting, storage, transportation and retrieval of rain water to obviate the need for dams and canals.
2. Prior Art
Superabsorbent polymers (SAP) are polymers that can absorb and retain extremely large amounts of a liquid relative to its own mass. Lightly cross-linked sodium polyacrylate is the most common type of SAP made in the world today. Widely used in personal disposable hygiene products such as baby diapers, it can absorb about 800 times its weight of distilled water. Other SAP compositions include acrylamide copolymers, ethylene maleic anhydride copolymers, crosslinked carboxy-methyl-cellulose, polyvinyl alcohol copolymers, crosslinked polyethylene oxide and starch grafted copolymer of acrylonitrile.
One of the early patents, U.S. Pat. No. 3,669,103, describes compositions based on lightly cross-linked polymers, such as polyvinylpyrrolidones, sulfonated polystyrenes, sulfonated polyvinyltoluenes, poly-sulfoethyl acrylates, poly-2-hydroxyethyl acrylates, polyacrylates, hydrolyzed polyacrylamides and copolymers of acrylamide with acrylic acid for use in diapers.
U.S. Pat. No. 3,935,099 describes alkali saponified gelatinized-starch-polyacrylonitrile graft polymers used as absorbents for aqueous suspensions such as sewage sludges.
U.S. Pat. No. 4,286,082 discloses lightly cross-linked sodium polyacrylate SAP for use in baby diapers and sanitary napkins.
In U.S. Pat. No. 4,483,950, starch-based superabsorbents extended with modified starches were promoted as thickening agents.
U.S. Pat. No. 4,913,517 covers uses of SAPs as cable-sealing materials.
U.S. Pat. No. 5,241,009 describes polycarboxyl group containing superabsorbents wherein neutralization of said carboxyl groups with potassium or lithium is described as providing a polymeric composition specifically adapted to absorb proteinaceous fluids, such as blood.
U.S. Pat. No. 6,623,645 describes use of SAPS for wastewater containment and treatment. It does not use stimuli-responsive SAPS. The water collected is contaminated and cannot be used by humans for normal use. It is not a method to replace dams and canals. The dry contaminated polymer is discarded and cannot be reused.
U.S. Pat. No. 6,869,464 describes a device for collecting atmospheric water at humid locations. It does not teach about collection of water in bags, their storage in warehouses or distribution. It is not a method to replace dams and canals.
U.S. Pat. No. 6,800,712 discloses SAPS based on grafted starches for use in crop production.
In all above examples, SAPS generally absorb up to 1000 times their weight of water.
Global demand for SAPS is about 2 million metric tons annually. More than 90% is used in disposable hygiene products. Small amounts are used in agriculture, cable sealing and other niche applications.
Recent research has resulted in some highly absorbent SAPs. Deyu in his Ph.D. thesis “Superabsorbent Polymer Composite Materials and their Industrial and High-Tech Applications”, 2003, at Technische Universitat, Bergakademie, Freiberg, Germany describes SAP composites with bentonite (clay) to have water absorbence in excess of over 2000 gram/gram of the composite.
Bowling Green State University in the US has reported water absorbance in the range of 2000 to 6000 grams/gram of SAP. The research is described in Thilini K. Mudiyanselage et al, Highly Absorbing Superabsorbent Polymer, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 46, 1357-1364 (2008). The same research team at the Bowling Green State University has also synthesized photochromic SAPs with water absorbance of 2800 g/g of SAP. When the hydrated photochromic SAP was irradiated with UV light, it expelled the water.
Hitherto, no one has proposed use of SAPs for harvesting and storage of rain water as replacement of dams and canals.